Add a patch to avoid scratching the CXXFLAGS in OpenBabel plugin.
blhc test is failing because of missing hardened CXXFLAGS when compiling the OpenBabel plugin.
I am emptying the CXXFLAGS in the Makefile.am of that plugin, because of some warnings reported by OpenBabel which didn't work well with -Werror being in the CXXFLAGS. But that is definitely the wrong way to get rid of these warnings becoming errors!
For the moment, I'm adding a patch to avoid the scratching of the flags. Hopefully this will solve the CI failure with blhc. And I'll find later a better way to get -Werror works in OpenBabel plugin.